>>8771518Problems are a mix of;
Manufacturer's not cutting the gas port to the correct size, causing over gassing.
Gases still running too fast for the weapon because of the shorter gas tube.
These cause the action to run faster than it should, causing a whole slew of problems like FTE, stovepipes, and even running over the cartridge before it has had time to be pushed into the ready position by the magazine.
The majority of these are solved by the mid-length system, and you only really should run a carbine length if you're barrel length forces you to (Read: 7/10" entry gun).
Remember, the AR-15 was designed for a 20" barrel with the rifle length gas system. The further you stray from that design, the more problems you encounter.
Common 'fixes' to the carbine problems are usually stronger magazine springs, heavier buffers (H/H2 buffers), and stronger buffer springs.